Kubera is the lord of wealth and ruling deity for the cardinal direction of North. He is also the chief of the demi-gods Yakshas. He appeared before Arjuna alongwith Indra and other gods when Arjuna undertook a successsful penance to satisfy Indra and Shiva. Then he awarded an asthra called Sammohanam to Arjuna which the later used it against the kouravas while fighting with them for Viraata's cows.
Also, Kubera appears in the story in the Aaranya Parva, when Bheema went for the divine Sougandhika flowers and foughr the Yakshas.
Kubera is son of Visravana and thus is a cousin of the demon king Raavana ( of the Raamaayanam) . He is the owner of the famous divine flyer Pushpakam. Other details like his first birth, curse from Paarvathi etc can be read elsewhere in puraanams.